[SOLVED] my last two double angle questions

I am pretty sure I'm almost done the first one.

#1

Use the identity for sin2x and an identity for cos2x to verify that http://www.sosmath.com/CBB/latexrend...c7327fd889.gif

but when I use the formula for double angles like where http://www.sosmath.com/CBB/latexrend...3887eaaaf8.gifwith a http://www.sosmath.com/CBB/latexrend...b5c1c816b4.gif

I think it is

http://www.sosmath.com/CBB/latexrend...451be35bae.gif

Thanks for any help you may have.

And

#2

how do you find roots/solve something like

or I algebraically? I have done questions where you have to do proofs, but I have no examples like this from my teacher, thanks.

sorry about the multiple questions but the site was down lol.